EFFECTS OF NORTHERN PIKE ON PATTERNS OF NEST USE AND REPRODUCTIVE-BEHAVIOR OF MALE FATHEAD MINNOWS IN A BOREAL LAKE

We conducted a two-part study to assess predator avoidance by reproduc tive male fathead minnows (Pimephales promelas) subjected to predation threat from northern pike (Esox lucius). First, we determined if patt erns of nest use by egg-guarding male minnows in a boreal lake were re lated to pike densities. We sampled northern pike and identified four areas of ''high pike-density'' and three areas of ''low pike-density.' ' We censused natural nests and placed nest boards in these areas. We found eggs on natural nests more frequently in areas with low densitie s of pike than in areas with high densities of pike. However, we could not fully explain the distribution of nests by predation risk. Second , we evaluated the behavioral response of egg-guarding males to a cont rol stimulus (a piece of wood) or a live pike in a wire cage. We used time to return to the nest after a stimulus as a measure of risk takin g. Males took different amounts of risk based on predation threat; mal es in the predator treatment took longer to return to their nests than control males. Risk taking was not related to the number or age of th e eggs but to distance to nearest egg-guarding neighbor; males with cl ose neighbors returned sooner than more isolated males. Males in the p redator treatment had lower total activity and egg rubbing than contro l males after they returned to their nests. We conclude that male fath ead minnows altered their reproductive behavior in ways that reduced p redation risk, but the cost of predator avoidance might include egg pr edation, lost mating opportunities, or usurpation of nests.